This study is based on the general hypothesis that elderly people with cardiovascular risk factors develop abnormalities in cerebral blood flow regulation, which threaten cerebral perfusion, produce subcortical white matter damage, and ultimately lead to the common geriatric syndromes of falls, slow gait, executive cognitive dysfunction, and depression. In Aim 1 we will assess longitudinally the a) risk factors and b) clinical outcomes associated with abnormal middle cerebral artery reactivity to CO2 and posture change in a representative elderly population using transcranial Doppler ultrasound (TCD). In Aim 2 we will determine the anatomical and cerebrovascular regulatory changes of the brain associated with slow gait speed in subgroups of the population, using quantitative magnetic resonance imaging and TCD. During the previous funding period we have developed the capacity to measure cerebral vasoregulation and blood flow responses to cognitive activation in specific regions of the brain. These techniques will enable us to move beyond descriptive studies of structural changes in the brain, to a dynamic assessment of cerebral blood flow responses to common daily tasks necessary for normal cognition and mobility. Our results will not only clarify the relationships between cerebral perfusion, white matter changes, and morbid clinical outcomes, but will also provide new approaches to the prediction and prevention of gait impairment, falls, executive dysfunction, and depression using non-invasive TCD measures of cerebrovascular function.